IPv6 Tunneling Techniques

A network engineer is troubleshooting an IPv6 connectivity issue between two sites connected via a 6to4 tunnel. The tunnel is configured on both routers and shows as up/up, but the engineer cannot ping the IPv6 address of the remote tunnel endpoint. The engineer checks the routing table and sees no route to the remote IPv6 prefix. What is the most likely cause of this problem?

An engineer is troubleshooting an ISATAP tunnel between a Windows host and a Cisco router. The host can ping the router's IPv6 address configured on the tunnel interface, but cannot reach any other IPv6 networks beyond the router. The router has a default route pointing to an upstream IPv6 router. What is the most likely cause?

A network engineer is troubleshooting a manual IPv6-in-IPv4 tunnel between two Cisco routers. The tunnel is up, and both routers can ping each other's tunnel IPv6 addresses. However, traffic from a host behind Router A to a host behind Router B fails. The engineer notices that Router A has a route to the remote IPv6 prefix via the tunnel, but Router B does not have a route to the local IPv6 prefix. What is the most likely cause?

An engineer is troubleshooting a GRE IPv6 tunnel between two sites. The tunnel is up, and the engineer can ping the remote tunnel endpoint IPv6 address. However, OSPFv3 neighbors over the tunnel fail to form. The engineer verifies that OSPFv3 is configured on both tunnel interfaces with the same area and that the network type is broadcast. What is the most likely cause?

A network engineer is troubleshooting an IPv6 connectivity problem across an IPv4 MPLS network using 6PE. The 6PE routers have MP-BGP sessions to exchange IPv6 prefixes, and the tunnel between them is up. However, a customer edge router behind one 6PE router cannot reach an IPv6 prefix behind the other 6PE router. The engineer checks the 6PE router's BGP table and sees the prefix, but the routing table shows the next-hop as unreachable. What is the most likely cause?

An engineer is troubleshooting a DMVPN phase 2 deployment with IPv6 over mGRE tunnels. The spoke routers can ping the hub's tunnel IPv6 address, but cannot reach IPv6 networks behind other spokes. The engineer verifies that NHRP is configured and that the hub has a route to the spoke's internal networks. What is the most likely cause?

A network engineer is troubleshooting an IPv6 over IPv4 tunnel using Teredo on a Windows host. The host can access some IPv6 resources on the internet but cannot reach a specific internal IPv6 server. The engineer suspects the Teredo relay is misconfigured. What is the most likely issue?

An engineer is troubleshooting an IPv6 manual tunnel between two routers that are not directly connected (the tunnel endpoints are separated by an IPv4 network). The tunnel is up, but the engineer notices that the tunnel interface flaps every few minutes. The show interfaces tunnel output shows input errors and CRC errors. What is the most likely cause?

A network engineer is troubleshooting an IPv6 over IPv4 tunnel that is used to connect two remote sites. The tunnel is configured with a tunnel source that is a loopback interface. The tunnel is up, but the engineer cannot ping the remote tunnel endpoint IPv6 address. The engineer checks the routing table and sees a route to the remote loopback's IPv4 address via a default route. What is the most likely cause?

A network engineer runs the following command on Router R1: R1# show ipv6 tunnel brief Tunnel2: IPv6/IP, intf id 0/0/2, 6to4, mtu 1280 Source: 192.168.1.1 (GigabitEthernet0/0) Destination: 192.168.2.1 Tunnel transport: IPv4 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ipv6 interface tunnel 0 Tunnel0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::A8BB:CCFF:FE00:1 No global unicast address is configured Joined group address(es): FF02::1 FF02::2 FF02::1:FF00:1 MTU is 1480 bytes ICMP error messages limited to one every 100 milliseconds ICMP redirects are enabled ICMP unreachables are sent ND DAD is enabled, number of DAD attempts: 1 ND reachable time is 30000 milliseconds ND advertised reachable time is 0 milliseconds ND advertised retransmit interval is 0 milliseconds ND router advertisements are sent every 200 seconds ND router advertisements live for 1800 seconds Hosts use stateless autoconfiguration for addresses. Based on this output, what is a likely problem?

A network engineer runs the following command on Router R1: R1# show ipv6 route | include Tunnel O 2001:DB8:1::/48 [110/2] via FE80::1, Tunnel0 O 2001:DB8:2::/48 [110/3] via FE80::2, Tunnel1 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ipv6 mld interface tunnel 0 Tunnel0 is up, line protocol is up Internet address is FE80::1 MLD is enabled on interface Current MLD version is 2 MLD query interval is 125 seconds MLD querier timeout is 255 seconds MLD max query response time is 10 seconds Last member query response interval is 1 second MLD activity: 0 joins, 0 leaves MLD querying router is FE80::1 (this system) Based on this output, what can be concluded?

A network engineer runs the following command on Router R1: R1# show ipv6 ospf neighbor Neighbor ID Pri State Dead Time Address Interface 192.168.1.2 1 FULL/DR 00:00:32 FE80::2 Tunnel0 192.168.1.3 1 FULL/BDR 00:00:35 FE80::3 Tunnel0 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ipv6 bgp summary BGP router identifier 192.168.1.1, local AS number 65001 BGP table version is 10, main routing table version 10 5 network entries using 720 bytes of memory 5 path entries using 400 bytes of memory 3/2 BGP path/bestpath attribute entries using 456 bytes of memory 1 BGP AS-PATH entries using 24 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 1600 total bytes of memory BGP activity 10/5 prefixes, 10/5 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 2001:DB8::2 4 65002 100 99 10 0 0 00:45:12 3 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ipv6 eigrp neighbors IPv6-EIGRP neighbors for process 100 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 FE80::A8BB:CCFF:FE00:2 Tunnel0 13 00:23:45 10 200 0 12 1 FE80::A8BB:CCFF:FE00:3 Tunnel1 12 00:22:10 15 200 0 15 Based on this output, which statement is correct?

A network engineer runs the following command on Router R1: R1# show ipv6 mtu IPv6 MTU per interface: Interface MTU Tunnel0 1476 Tunnel1 1476 GigabitEthernet0/0 1500 Based on this output, what is the most likely reason for the reduced MTU on the tunnel interfaces?

A network engineer runs the following command on Router R1: R1# show ipv6 traffic | include tunnel 0 tunnel packets received 0 tunnel packets sent 0 tunnel packets dropped Based on this output, what can be concluded?

Examine the following partial configuration on Router R1: ``` interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source GigabitEthernet0/0 tunnel destination 2001:DB8:2::2 tunnel mode ipv6ip ``` What is the effect of this configuration?

Consider this configuration on Router R2: ``` interface Tunnel0 ipv6 address 2001:DB8:3::1/64 tunnel source GigabitEthernet0/0 tunnel mode gre ipv6 tunnel destination 2001:DB8:4::2 ``` Which statement is true?

Given this configuration on Router R3: ``` interface Tunnel0 no ip address ipv6 address 2001:DB8:5::1/64 tunnel source 192.168.1.1 tunnel destination 192.168.2.2 tunnel mode ipv6ip ``` What is missing or incorrect?

Examine this configuration on Router R4: ``` interface Tunnel0 ip address 10.0.0.1 255.255.255.252 ipv6 address 2001:DB8:6::1/64 tunnel source GigabitEthernet0/0 tunnel destination 172.16.1.2 tunnel mode gre ip ``` What will be the effect?

Consider this configuration on Router R5: ``` interface Tunnel0 ipv6 address 2001:DB8:7::1/64 tunnel source 192.168.10.1 tunnel destination 192.168.20.2 tunnel mode ipv6ip tunnel ttl 64 ``` What is the effect?

Given this configuration on Router R6: ``` interface Tunnel0 ipv6 address 2001:DB8:8::1/64 tunnel source 2001:DB8:9::1 tunnel destination 2001:DB8:10::2 tunnel mode gre ipv6 tunnel path-mtu-discovery ``` What is the effect?

What is the default tunnel mode for a tunnel interface on Cisco IOS?

In a 6to4 tunnel, how is the tunnel destination address determined?

What is the maximum number of IPv6 over IPv4 tunnels that can be configured on a Cisco IOS router?

Which TWO commands can be used to verify the operational status of a manually configured IPv6 tunnel on a Cisco IOS router? (Choose TWO.)

A large enterprise network is experiencing intermittent IPv6 connectivity between two remote sites connected via an IPv6-in-IPv4 manual tunnel. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 ipv6 route 2001:DB8:2::/64 Tunnel0. Router R2 shows: R2# show ipv6 route 2001:DB8:1::/64 % Route not found. The tunnel interface is up/up on both routers, and IPv4 reachability between tunnel endpoints is verified. What is the root cause?

A DMVPN phase 3 network with IPv6 over IPv4 tunnels is experiencing spoke-to-spoke tunnel failures. Hub router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp map multicast dynamic ipv6 nhrp map multicast dynamic. Spoke router R2 shows: R2# show dmvpn detail Legend: Attrb -> S: Static, D: Dynamic, I: Incomplete NHRP domain: 1 Interface: Tunnel0, IPv4 NHRP Details Type:Spoke, Total NBMA Peers: 1 # Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb 1 192.0.2.2 2001:DB8:1::2 UP 00:10:00 D. What is the root cause?

An MPLS network with IPv6 over MPLS (6PE) is experiencing loss of IPv6 routes from a remote provider edge (PE) router. Router PE1 has the following relevant configuration: interface GigabitEthernet0/0 ipv6 address 2001:DB8:1::1/64 mpls ip interface Loopback0 ip address 192.0.2.1 255.255.255.255 router ospf 1 router-id 192.0.2.1 redistribute bgp 65000 subnets. Router PE2 shows: PE2# show bgp ipv6 unicast 2001:DB8:2::/64 % Network not in table. PE2# show mpls forwarding-table 192.0.2.1 Label: 16, Interface: GigabitEthernet0/1. What is the root cause?

A dual-stack network using IPv6 over IPv4 GRE tunnels with OSPFv3 is experiencing routing loops. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 ipv6 ospf network point-to-point ipv6 ospf 1 area 0. Router R2 shows: R2# show ipv6 ospf neighbor Neighbor ID Pri State Dead Time Interface ID Interface 192.0.2.2 1 FULL/ - 00:00:33 7 Tunnel0. R2# show ipv6 route 2001:DB8:3::/64 O 2001:DB8:3::/64 [110/2] via 2001:DB8:1::1, Tunnel0. What is the root cause?

An enterprise is using IPv6-to-IPv4 translation tunneling (NAT64) but users report that they cannot reach IPv6-only servers. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 nat64 enable. Router R2 shows: R2# show nat64 translations % No translations. R2# debug nat64 all NAT64: No mapping found for packet. What is the root cause?

A network using IPv6 over IPv4 ISATAP tunnels is experiencing connectivity issues. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::/64 eui-64 tunnel source 192.0.2.1 tunnel mode ipv6ip isatap. Router R2 shows: R2# show ipv6 interface Tunnel0 Tunnel0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::5EFE:192.0.2.2 Global unicast address(es): 2001:DB8:1::5EFE:192.0.2.2. What is the root cause?

A service provider is using 6rd (IPv6 Rapid Deployment) tunnels to provide IPv6 to customers. Customer router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel mode ipv6ip 6rd ipv6 6rd prefix 2001:DB8::/32 6rd-br 198.51.100.1. Router R2 (BR) shows: R2# show ipv6 route 2001:DB8:1::/64 % Route not found. What is the root cause?

A network using IPv6 over IPv4 L2TPv3 tunnels is experiencing packet drops. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 tunnel mode l2tpv3 ipv6. Router R2 shows: R2# show l2tp tunnel Tunnel id 1, 1 session Session id 1, state established. R2# show ipv6 interface Tunnel0 Tunnel0 is up, line protocol is up. What is the root cause?

A network using IPv6 over IPv4 Teredo tunnels is experiencing intermittent connectivity. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:0:4136:E378:8000:63BF:3C57:DD0B/128 tunnel source 192.0.2.1 tunnel mode ipv6ip teredo. Router R2 shows: R2# show ipv6 route 2001:0:4136:E378::/64 % Route not found. What is the root cause?

What is the default tunnel mode for an IPv6 tunnel configured on Cisco IOS-XE?

In a 6to4 tunnel, what is the default IPv6 prefix assigned to the tunnel interface?

What is the default keepalive interval for a GRE tunnel interface on Cisco IOS-XE?

Which statement correctly describes the behavior of ISATAP tunneling regarding host configuration?

In a manual IPv6 over IPv4 tunnel (tunnel mode ipv6ip), what is the default maximum number of hops (TTL) for the IPv4 header?

Which loop prevention mechanism is inherent to 6to4 tunneling?

What is the default metric for a static route pointing to a tunnel interface in Cisco IOS-XE?

Which authentication method is supported by default for GRE tunnels in Cisco IOS-XE?

What is the default IPv6 hop limit for packets sent over a tunnel interface in Cisco IOS-XE?

Drag and drop the steps to configure a GRE tunnel for IPv6 over IPv4 into the correct order, from first to last.

Drag and drop the steps to troubleshoot IPv6 over IPv4 tunnel adjacency or connectivity failures into the correct order, from first to last.

Drag and drop the steps to verify and validate the operational state of an IPv6 tunneling technique into the correct order, from first to last.

Which TWO statements correctly describe the behavior of automatic 6to4 tunneling? (Choose TWO.)

Which TWO actions will prevent an ISATAP tunnel from forming correctly? (Choose TWO.)

An engineer must configure a GRE tunnel to transport IPv6 traffic over an IPv4-only network. Which TWO configuration steps are required? (Choose TWO.)

Which THREE commands can be used to verify the operational state and configuration of an IPv6 tunnel? (Choose THREE.)

Which TWO statements about IPv6 manual tunnels (IPv6-in-IPv4) are true? (Choose TWO.)

An engineer configures an IPv6 manual tunnel between two routers. The tunnel comes up and pings succeed, but OSPFv3 over the tunnel fails to form an adjacency, stuck in EXSTART state. MTU is set to 1500 on all physical interfaces. What is the most likely cause?

A network engineer configures a 6to4 tunnel between two sites. The tunnel works for traffic from Site A to Site B, but return traffic from Site B to Site A fails. Both sites have IPv4 connectivity. What is the most likely explanation?

An engineer configures an ISATAP tunnel on a router. The tunnel comes up and the router can ping the ISATAP server, but IPv6 hosts on the ISATAP network cannot reach IPv6 hosts on the native IPv6 network. The ISATAP router is configured with a static route to the native network. What is the most likely cause?

A network engineer configures an IPv6 over IPv4 GRE tunnel with IPsec protection using a transform set that includes ESP encryption and authentication. The tunnel comes up, but OSPFv3 over the tunnel fails to form adjacency. The engineer notices that the tunnel interface has an MTU of 1400. What is the most likely explanation?

An engineer configures an IPv6 manual tunnel between two routers. The tunnel is up, but when the engineer tries to ping the IPv6 address of the remote tunnel endpoint, the ping fails. The engineer checks the routing table and sees that the remote IPv6 network is reachable via the tunnel. What is the most likely cause?

A network engineer configures an IPv6 over IPv4 GRE tunnel with IPsec protection. The tunnel works for IPv6 traffic, but when the engineer tries to run EIGRP for IPv6 over the tunnel, the neighbor relationship forms but routes are not exchanged. The engineer checks the EIGRP configuration and sees that the tunnel interface is included in the EIGRP process. What is the most likely explanation?

An engineer configures a 6rd tunnel on a router. The tunnel comes up and the router can reach IPv6 hosts on the 6rd domain, but IPv6 hosts behind the router cannot reach the internet (native IPv6). The 6rd border relay is configured correctly. What is the most likely cause?

A network engineer configures an IPv6 over IPv4 GRE tunnel with IPsec using a crypto map. The tunnel works for unicast traffic, but OSPFv3 over the tunnel fails to form adjacency. The engineer checks the crypto map and sees that it only matches traffic with a specific access-list. What is the most likely explanation?

An engineer configures an IPv6 manual tunnel between two routers. The tunnel is up and both routers can ping each other's tunnel IPv6 addresses. However, when the engineer tries to redistribute a connected IPv6 route from the tunnel into OSPFv3, the route is not advertised. The OSPFv3 process includes the tunnel interface. What is the most likely cause?